MARMET- METEORITES

The Allende Meteorite (Mexico)

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allende175g.jpg
Allende CV3.2; Mexico; fell 1969, 175 g, individual; ex coll. Dr. E. Moser, Switzerland.

The Allende meteorite - Chihuahua district, Mexico - fell on February 8, 1969 after a bright bolide was seen in the very early morning hours. It turned out to belong to the relatively rare class of meteorites - the carbonaceous chondrites - and was found in a strewn field estimated to cover over 250 km2. The ellipse was 50 km long and 12 km wide. More than two metric tons of the meteorite have been collected in hundreds of fragments, the largest of which had a mass of about 110 kg but unfortunately broke up on impact.

allende17.8g.slice.jpg
Allende CV3.2; Mexico; fell 1969, 17.8 g, slice full of interesting inclusions.

The Allende meteorite fell just a few months before the Apollo 11 astronauts landed on the Moon, providing a unique opportunity for scientists to test many of the analytical techniques that they had developed to study the lunar samples.

Allende is a rare type of meteorite, a carbonaceous chondrite, so called because it is rich in carbon. Allende contains CAIs, calcium-aluminum inclusions, predominantly white to light gray in color, irregularly shaped, and rich in refractory (high-temperature) minerals and they are thought to have formed at the very beginning of the solar system about 4567 million years ago. In addition, Allende has many well defined, more or less spheroidal chondrules. Both, the chondrules and the CAIs formed during rapid heating events at the dawn of the solar system. Numerous analyses indicate that CAIs formed about two million years earlier than chondrules. Relict pieces of CAIs have even been found inside chondrules, and so must have formed earlier. However, rather strange is the fact, that two Japanese scientists of the Tokyo Institute of Technology found a chondrule inside a CAI, which strongly indicates that some chondrules must have formed before CAIs... 

(a) shows amoeboid olivine aggregates, (b) an orthopyroxene rich chondrule, (c) might be a CM inclusion, (d) a melilite-fassaite-anorthite chondrule. 

allende.twins.8.7g.jpg
Allende CV3.2; Mexico; fell 1969, 4.0 g and 4.7 g.

allende15.7g.02.jpg
Allende CV3.2; Mexico; fell 1969, 15.7 g, slice with interesting inclusions.

allende15.7g.01.jpg
Allende CV3.2; Mexico; fell 1969, 15.7 g, "back side".

From: Bert King, MOON TRIP, 1989 pp. 82-86.

"While unsuccessfully searching for a meteorite fall close to Crosby, Texas, I heard on the car radio about a very bright fireball witnessed in southern New Mexico, Texas, and northern Mexico. I returned to my office and asked my secretary, who was fluent in Spanish, to place some phone calls for me. I first contacted a newspaper editor in Chihuahua City. We had a lengthy conversation about the phenomena accompanying the meteorite fall but no specimens had fallen near Chihuahua City. Finally, I asked him the right question: "Do you know anyone who has any pieces of the meteorite?" "Oh yes," he said, and suggested that I call the newspaper editor in Hidalgo del Parral, much further to the south. My secretary located Sr. Ruben Rocha Chavez, editor of Correa del Parral. He recounted how a brilliant fireball had broken apart with a loud explosion in the middle of the night and had showered fragments over a large area near Parral. Chavez had several pieces of the meteorite on his desk and described them to me. There was no doubt - he had fragments of a freshly fallen stony meteorite! He invited me to visit Parral to see his pieces and to collect specimens. I thanked him for the information and his invitation and told him I would be there as soon as possible.

A quick check of airline schedules showed it was not going to be easy to get to Parral. I could fly to El Paso, but that was still more than three hundred miles north of Parral. It was the fastest way, however. My secretary promised to cover me with paperwork. I stopped by my house for a few clothes and headed for the airport.

The plane took off on time, but, as luck would have it, a faulty landing gear indicator light grounded us in San Antonio for five hours while it was replaced. By the time I arrived in El Paso it was already dark. I picked up a rental car, cleared through customs, and drove south. It was important to recover pieces of the meteorite right

away in order to measure their short half-life radioactivities. This would be great practice for the Radiation Counting Laboratory of the LRL. The Mexican highways were difficult to negotiate in the dark. The best technique was to follow a hundred yards behind a car with Mexican license plates. Some of the drivers were going 80 miles per hour, and when I saw brake lights or a cloud of dust, I knew the driver had spotted a burro on the highway. I arrived in Parral just after dawn. I checked into a hotel, washed up, drank some strong coffee, ate eggs and tortillas, and went to look for the newspaper office. I was waiting when the editor arrived. I was astonished when I saw the two big meteorite pieces on the editor' s desk. One weighed more than 30 pounds. 

The greatest surprise was the meteorite type - a rare carbonaceous chondrite. Chondrites are stony meteorites that contain chondrules, small spheres of silicate of disputed origin. Carbonaceous chondrites are chondrites that contain abundant carbon and organic compounds. While I was standing in Chavez' office, the telephone rang. The editor handed the receiver to me. It was a colleague from the Smithsonian who wanted information about the meteorite. He had called my Houston office, where my secretary gave him the number of the newspaper office. I told him what little I knew. I asked the editor about his plans for the two specimens on his desk. He said they were reserved for the National Museum. I agreed this was perfectly appropriate, but I was eager to recover some additional specimens. The editor said I must visit the local municipal president or mayor. I was going to be treated as an official NASA representative.

The mayor, Sr. Carlos Franco, was extremely gracious, and though my Spanish was meager and he spoke little English, we had an amiable meeting. I explained, through the editor as translator, how scientifically important meteorites are in general and that this particular one was a very rare type. Sr. Franco was eager to help me, and he assigned me one of his policemen and an official car for as long as I needed them.

We drove to places where specimens had been found. Recovering additional specimens proved to be easy. Everyone had small pieces of the meteorite, but I wanted some larger ones. I purchased these from the local people, with the policeman acting as interpreter and handling the negotiations. We documented several sites where specimens had been found. The stones had showered over a large area. One large stone had missed the post office in Pueblito de Allende by only 30 feet. Meteorites normally are named after the nearest post office. This one almost named itself. We listened to many tales of the fireball, its direction of travel, the loud claps of thunder, stones falling everywhere, and people running to the church in the middle of the night. I picked up 13 pieces of the

meteorite, including two large ones - enough samples for the time being. 

allende.32.1g.a.jpg
Allende CV3.2; Mexico; fell 1969, 32.1 g, this slice was part of the King Collection of Meteorites.

By late afternoon, the day began to seem very long. I had not slept in 30 hours, and I still had to drive back to El Paso. We stopped at a little cantina, and I bought drinks for the meteorite party - the policeman, a local engineer who had been very helpful, and the Mexican reporters who had followed us all day. I bid them adios and hoped to make it to El Paso before nightfall. I pinched my arms and bit the back of my hand to stay awake. I arrived in El Paso after dark and entered U.S. Customs. I was met by a young customs agent who had taken a course in geology and wanted to know about the rocks I had. I finally reached the airport, turned in the rental car and inquired if an one from Washington had made car reservations. Two of my Smithsonian friends had reserved cars, so I left them a long note telling them who to see and where to go to recover additional meteorites. I called Houston and told them to get the lab ready. I dozed for several hours in the airport until boarding time and then slept all the way to Houston.

One hundred and one hours after the fall we were gathering data on a piece of the Allende meteorite in the LRL low-background gamma-ray counter." The Allende meteorite proved to be a ”gold mine" of meteoritical science. We distributed many pieces to various investigators, using the procedure as a dress rehearsal for the lunar sample analyses. My own work with Allende would have to wait. It was too close to arrival time of the first lunar sample, and a lot of work remained to be done at the LRL. Allende became the best known and most studied meteorite in history."

allende19.5g.jpg
Allende CV3.2; Mexico; fell 1969, 19.5 g, end cut, interesting inclusions.

allenden.asu.1.jpg
Allende CV3.2; Mexico; fell 1969, 93.41 g, this slice was used by John T. Wasson in his research!

allende.ts.jpg
Thin section of the Allende meteorite.